~ Common Emitter Amplifier ~ Transistor r_bb Calculator ~

To be used with a Common Emitter test jig as described Here
Boltzmann Constant — k	1.3806x10-23	J/K    [ Joules/Kelvin ]
Charge on a single Electron — q	1.6022x10-19	C   [ Coulomb or Amperes/sec ]
Measurement device load — RL		Ω Parallel with RC assumed a.c. coupled
Collector Resistor — RC		Ω Load resistor  [ RE & RS assumed = 0 ]
Measured Voltage across RC — VRC		V     IC = VRC/RC = mA
Measured Voltage Gain		AVm  [ affected by high rbb and low ro ]
Noise Voltage at Collector — VNtot		µVrms  Enter Measured value @ IC T & Bn
Transistor d.c. current gain — β		hFE from data sheets @ IC or measured
Device Temperature — T		˚C    Calculation uses  T =  ˚K
Measurement Noise Bandwidth — Bn		Hz — Is not the –3dB BW see Here
Calculated results using the values entered above
Voltage Gain neglecting ro — AV		V/V = α RC/re
Emitter Internal Resistance — re		Ω = VT/IC     VT = kT/q =
Load resistor including ro — RCm		Ω                     RC || RL =  Ω
Internal Collector Resistor — ro		kΩ              VA = ro • IC =  V
Noise at Collector due to IC — VNIC		µVrms = √2 q IC Bn  • (RCm–re)
Noise at Collector due to RCm — VNRC		µVrms = √4 k T Bn RCm
Noise at Collector due to rbb		µV = √V2Ntot–V2NRC–V2NIC = √V2Nrbb+V2NIB
rbb calculated from √V2Nrbb+V2NIB		Ω              The –ve result

The value of R_C modified by r_o [R_Cm] must be less than the total collector load R_C || R_L ~ The calculated value of r_bb must be positive and the negative result negative for the answer to be plausible ~ NaN [Not a Number] may indicate the measured gain or other inputs are not correct or a non numeric input was entered

See also ~ r_bb calculated from data–sheet values  but beware some data–sheet figures may not be in the units you need

 

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